1. Field of the Invention
The present invention relates to a thermal image transfer recording medium comprising a support and a thermofusible ink layer formed thereon, comprising as the main components a coloring agent and a binder agent, which is capable of yielding excellent transferred images on any image-receiving sheet, and suitable for use with printers for computers and word processors, and a bar code printer.
2. Discussion of Background
Recently a thermal image transfer recording system using a thermal head is widely used because of the advantages that it is noiseless, the apparatus for use in the system is relatively inexpensive and can be made small in size, the maintenance is easy, and printed images are stable in quality.
Representative examples of thermal image transfer recording media for use with such a thermal image transfer recording system are as follows:
(1) A thermal image transfer recording medium comprising a support and a thermofusible ink layer which is directly provided on the support, and comprises a coloring agent and a binder agent.
(2) A thermal image transfer recording medium in which a release layer and a thermofusible ink layer are successively overlaid on a support. The release layer essentially consists of a wax component, while the thermofusible ink layer essentially consists of a coloring agent and a binder agent.
However, the above-mentioned conventional thermal image transfer recording media still have the shortcomings in the image transfer ratio and the resolution of the transferred image, depending on the structure of the layers and the kind of the constituents of the recording medium.
More specifically, the ink layer and the release layer of the aforementioned thermal image transfer recording media (1) and (2) are prepared by the hot-melt coating of the constituents such as a wax, a resin or a coloring agent, or by coating a solution or dispersion of those constituents which are dissolved or dispersed in an aqueous or nonaqueous solvent and completely removing the solvent component such as water or an organic solvent. Therefore, the thermofusible ink layer and the release layer are lipophilic, while an image-receiving sheet to which an image is to be transferred from the thermal image transfer recording medium is hydrophilic. As a result, the affinity of the ink contained in the thermofusible ink layer for the image-receiving sheet is decreased, so that the image transfer efficiency is lowered and partial missing of printed images is induced.
Furthermore, when the image-receiving sheet is a sheet of synthetic paper, for example, prepared by kneading a lublicant into a polyethylene film, such as a commercially available synthetic paper "Yupo" (Trademark), made by Oji-Yuka Synthetic Paper Co., Ltd., which easily absorbs the water content, it is considerably difficult to successfully transfer an ink component mainly comprising the oil-type wax to that kind of image-receiving sheet.
To solve the above shortcomings, there is proposed a thermal image transfer recording medium which comprises a thermofusible ink layer containing a polyhydric alcohol, as disclosed in Japanese Laid-Open Patent Application 58-129074. When images are transferred to a sheet of paper with a rough surface by using the above-mentioned thermal image transfer recording medium, voids easily occur. In the case where a sheet of synthetic paper is used as an image-receiving sheet, the image cannot satisfactorily be transferred to the image-receiving sheet and, in addition, a portion of the thermofusible ink layer to which the thermal energy from a thermal head is not applied is also transferred to the image-receiving sheet.